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    20 December 2017 Volume 44 Issue 6
      
    Optimization model of the irregular multi-level fat-tree network
    XU Zhanqi;WANG Na;YANG Fan;ZHANG Yushuai
    Journal of Xidian University. 2017, 44(6):  1-7.  doi:10.3969/j.issn.1001-2400.2017.06.001
    Abstract ( 352 )   PDF (589KB) ( 540 )   Save
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    To reduce the cost of traditional fat-tree networks, an irregular multi-level fat-tree network (IMLFTN) is proposed, with its network node using a special basic switching module (BSM) in which the number of upward ports is fixed while the number of downward ports remains variable. Analyzing the switching mechanism and traffic distribution of each BSM, the cost function of a BSM considers its numbers of upward and downward ports, and the traffic through it as well. The BSMs used at the first level are chosen according to the total number of users, and the BSMs located at other levels are accordingly determined and connected together to form an IMLFTN. The optimal IMLFTN is selected by the total cost of all IMLFTNs constructed by the combination of BSMs with different numbers of ports. Numerical results show that the proposed IMLFTN has a large advantage in cost when constructing the network with the same number of users.

    Blind recognition algorithm for IRA codes in noisy environment
    CHEN Jian;GUO Yongbin;WANG Yantao;KUO Yonghong
    Journal of Xidian University. 2017, 44(6):  8-13.  doi:10.3969/j.issn.1001-2400.2017.06.002
    Abstract ( 246 )   PDF (889KB) ( 290 )   Save
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    For noisy environment, the parity-check matrix of Irregular Repeat-Accumulate(IRA) codes is hard to reconstruct, moreover, the relationships of the large-scale complex interleaver are hard to recover. To solve the problems, a novel blind recognition algorithm is proposed. First, the code's length and synchronization are identified by applying rank criteria. Second, by implementing matrix transformation, the dual vectors of codewords are found. Then, by setting a threshold, the effective parity-check vectors of dual space are selected. According to the sparse characteristics of the IRA codes' parity-check matrix, the parity matrix can be reconstructed with effective parity-check vectors Finally, relationships of the interleaver can be recovered according to the characteristics of IRA codes. Simulation results show that the proposal can be used to estimate IRA codes encoding parameters and complete the blind recognition in the non-cooperative context with noise.

    Estimation of access failure probability in D2D underlaid cellular networks
    SUN Peng;ZHANG Hailin
    Journal of Xidian University. 2017, 44(6):  14-19.  doi:10.3969/j.issn.1001-2400.2017.06.003
    Abstract ( 338 )   PDF (1123KB) ( 264 )   Save
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    Device-to-Device (D2D) communication can reduce the mobile devices' energy consumption and increase the spectral efficiency in D2D underlaid cellular networks. However, D2D users will interfere with co-channel cellular users, which can lead to cellular communication access failures. There are two reasons for cellular communication access failures: (1)D2D interference and (2)insufficient spectrum resources. To address the absence of research on the performance of cellular services' access in D2D underlaid cellular networks, this paper defines the new services' access failure probability and handoff services' access failure probability to evaluate the effect of both D2D interference and limited resources on cellular communication access. Based on the stochastic geometry and stochastic process, a random network model is presented to estimate the access failure probabilities, which can provide guidelines for network design to ensure cellular services' access. The accuracy of the estimated access failure probability is validated through extensive simulations.

    Variable sorting based on fault tree structure adjustment for multi-valued decision diagrams
    FANG Min;ZHOU Shuyue;CHEN Yongmei;WANG Hongchun;QIU Zheng;ZHANG Zhendong;XIAO Chenguang
    Journal of Xidian University. 2017, 44(6):  20-25+36.  doi:10.3969/j.issn.1001-2400.2017.06.004
    Abstract ( 296 )   PDF (563KB) ( 225 )   Save
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    The dynamic fault tree does not have the ability of fault calculation when analyzing the reliability of the system, so it needs to be modeled and analyzed by means of multi-valued decision diagrams and so on. The dynamic fault tree is translated into a multi-valued decision diagram according to the ordering of variables of basic events which affects the size of the generated multi-valued decision diagram and the cost of traversal to get cut sequences. An adjustment method of the dynamic fault tree structure is proposed based on the importance degree of repeated events, dynamic gates and the locations of events of the dynamic fault tree. By taking the fact that the basic events at the same level are equally important into account, an improved dynamic variable ordering method and ordering generation algorithm for the multi-valued decision diagram are presented in this paper. The result analysis of an example shows that the improved dynamic variable ordering method can reduce the size of the multi-valued decision diagram and space and time complexity of the reliability calculation compared to the similar methods.

    Improved stochastic subspace method for identifying structural modal parameters
    LI Tuanjie;LIU Weimeng;TANG Yaqiong;GAO Liqiang
    Journal of Xidian University. 2017, 44(6):  26-30+58.  doi:10.3969/j.issn.1001-2400.2017.06.005
    Abstract ( 306 )   PDF (876KB) ( 260 )   Save
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    Stochastic subspace identification can be used to identify the modal parameters of a structure according to its dynamic response to ambient excitation. However, some high dimensional matrices (Toeplitz matrices) must be constructed in the process of identification, and lots of memory and computation time are cost to the singular value decomposition of these high dimensional matrixes. Stochastic subspace identification affects the computational efficiency seriously. Therefore, this paper investigates a new method for constructing lower-dimension Toeplitz matrices to improve the computing efficiency. Finally, a numerical simulation is presented to demonstrate the computing efficiency of the method. The result shows that the computing consumption of the proposed method is only 106% the computing consumption of the traditional stochastic subspace identification while the identification accuracy is maintained.

    Multiple maneuvering extended targets tracking with Gaussian process regression
    LI Cuiyun;WANG Jingyi;JI Hongbing
    Journal of Xidian University. 2017, 44(6):  31-36.  doi:10.3969/j.issn.1001-2400.2017.06.006
    Abstract ( 393 )   PDF (608KB) ( 228 )   Save
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    In view of the complexity of estimating the shape of the extended target and the low accuracy in multiple maneuvering extended targets tracking in the clutters, a multiple maneuvering extended targets tracking algorithm with Gaussian Process Regression is proposed. First, the extension of targets is modeled as a star-convex model. Then, the concept of weights used in the multiple targets tracking algorithm is introduced to the single maneuvering extended target tracking algorithm to realize multi-targets tracking. Finally, the Gaussian Process Regression is used to estimate the shape for the extended target. Simulation shows that the proposed algorithm is capable of tracking multiple maneuvering extended targets in the same scene with different shapes, and outperforms the traditional non-ellipsoidal extended target tracking algorithm in the estimation precision and computing speed.

    Method of co-channel interference cancellation for the GSM based PBR
    CHEN Gang;WANG Jun;WANG Jue;GUO Shuai
    Journal of Xidian University. 2017, 44(6):  37-42.  doi:10.3969/j.issn.1001-2400.2017.06.007
    Abstract ( 406 )   PDF (1626KB) ( 221 )   Save
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    In passive bistatic radar, especially in the global system for mobile communication based passive bistatic radar, there are not only strong direct signal and multipath, but also co-channel interference. It is difficult to suppress co-channel interference using temporal adaptive cancellation without the samples of interference. Aiming at the problem of co-channel interference signals existing in the echo channel, a method of co-channel interference cancellation for passive bistatic radar is proposed. First, low sidelobe spatial filtering is used to remove the remote weak interference, at the same time the strong interference is suppressed to a certain extent. Then, the direct signal and multipath signal coming from the main station are suppressed by using temporal adaptive cancellation. Finally, the remaining interference is further cancelled by a robust adaptive beamformer. The performance and calculation of the proposed method are verified by theoretical analysis and simulation.

    Component number estimation of time-frequency overlapped signals in underlay cognitive radio
    LIU Mingqian;CHEN Qian;WU Yun;WANG Jianghong
    Journal of Xidian University. 2017, 44(6):  43-47+64.  doi:10.3969/j.issn.1001-2400.2017.06.008
    Abstract ( 301 )   PDF (653KB) ( 148 )   Save
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    This paper proposes a novel method to estimate the number of signal components of time-frequency overlapped signals in low signal to noise ratio environment of the underlay spectrum sharing mode. First, the virtual array signal is constructed by dynamic delay, and then the feature quantity and estimation criterion are constructed by using the characteristic that the noise singular value is not changed very much, and the number of signal components of time-frequency overlapped signals in the underlay spectrum sharing mode is estimated. Simulation results show that the performance of the proposed method is better than that of the existing methods under the conditions of low SNR and high spectrum overlapped rates.

    Integration of the radar and communication method with FRFT-OFDM signals
    GU Yabin;ZHANG Linrang;ZHOU Yu
    Journal of Xidian University. 2017, 44(6):  48-52+84.  doi:10.3969/j.issn.1001-2400.2017.06.009
    Abstract ( 332 )   PDF (940KB) ( 181 )   Save
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    A transmitted pattern based on pulsed fractional Fourier transform OFDM is designed to realize the integration of radar and communication. In this designed pattern, radar transmits the FRFT-OFDM pulse, and the communication function is realized within the pulse. Multiple scatter radar signal processing based on maximum likelihood is proposed. The received signal can be written as the convolution of the transmitted sequence and the weighted RCS coefficient after sampling the received signal with a certain delay, then the maximum likelihood method is applied to get the range reconstruction. Finally, FFT is applied along the pulses within a coherent processing interval. Theoretical analysis and simulation results indicate that the proposed method can improve bit error rate performance and obtain multiple scatter range reconstruction and velocities estimation.

    Single-fed low-profile dual-band circularly polarized antenna
    YANG Mudan;ZHANG Fushun;ZHANG Fan;WANG Danyang
    Journal of Xidian University. 2017, 44(6):  53-58.  doi:10.3969/j.issn.1001-2400.2017.06.010
    Abstract ( 568 )   PDF (2907KB) ( 315 )   Save
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    In order to reduce the profile of the multi-layer structure and the complexity of the power dividing network of the dual-frequency dual-fed circular polarized (CP) antenna, a dual-band circularly polarized microstrip antenna is designed with a single-fed single-layer structure. It has two types of pattern of omnidirectional circular polarization and broadside circular polarization in two operating bands. A combination of an Alford loop and a shorting metallic cylinder loaded in the center of the patch is uesd to excite omnidirectional circular polarization in the low operating band; and a circular patch with a pair of symmetric rectangular slots is adopted to obtain circular polarization in the high operating band. The antenna prototype is fabricated and measured. Measured results show that the designed antenna has impedance bandwidths of 75% (242~261GHz) and 103% (332~368GHz) (reflection coefficient<-10dB). Axial ratio (AR) bandwidths are 4% (244~254GHz) and 23% (346~354GHz) (AR<3dB), respectively. The gain variations within two operating bands are less than 04dB. This antenna can be applied to the 25/35GHz frequency band of Worldwide Interoperability for the Microwave Access (WiMAX) system.

    POLSAR image classification via high-probability selection and adaptive MRF
    ZHANG Shuyin;HOU Biao
    Journal of Xidian University. 2017, 44(6):  59-64.  doi:10.3969/j.issn.1001-2400.2017.06.011
    Abstract ( 285 )   PDF (4813KB) ( 202 )   Save
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    It is difficult to obtain the accurate boundaries and the smooth regions for polarimetric SAR image classification. In order to solve this problem, a novel classification scheme is proposed that combines the Wishart-based high-probabilistic support vector machine (SVM) and adaptive markov random fields(MRF). First, a Wishart classifier is applied with the probabilistic SVM, according to high-probalistic selection, an initial pixel-based classification result is obtained. Then by combining this result with other edge detection methods, it can access the accurate boundaries. Second, adaptive MRF is proposed based on the edge of the image to further revise the previous classification. In this way, smooth regions are obtained and accurate boundaries are maintained simultaneously. Experimental results show that the proposed method improves the classification performance and that details of the image are preserved.

    Parallel FDTD computation of million cores with the domestically-made many-core supercomputer
    JIANG Xuesong;JIANG Shugang;ZHANG Yu;ZHAO Xunwang
    Journal of Xidian University. 2017, 44(6):  65-69+128.  doi:10.3969/j.issn.1001-2400.2017.06.012
    Abstract ( 382 )   PDF (1392KB) ( 195 )   Save
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    According to the new structure of domestically-made super computers, the massively parallel Finite-Difference Time-Domain (FDTD) is studied. By using the accelerating thread library, a parallel FDTD programming method for many-core processors is proposed. The parallel FDTD program based on this method is the first to realize 3 million processor cores parallel computation.Test results show that the parallel efficiency can reach up to 50% on 327680 cores with 16384 cores as the benchmark. And an analysis of the 200 wavelength electric size airborne antenna array is made. The researches in this paper indicate that the complicate electromagnetic problems can be solved efficiently using the method on the domestic many-core supercomputing platform.

    Bidirectional current path recessed gate tunnel field-effect transistor
    CHEN Shupeng;WANG Shulong;LIU Hongxia;LI Wei;WANG Xing;WANG Qianqiong
    Journal of Xidian University. 2017, 44(6):  70-74+168.  doi:10.3969/j.issn.1001-2400.2017.06.013
    Abstract ( 357 )   PDF (1953KB) ( 205 )   Save
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    The structure asymmetry of the conventional tunneling transistor makes it only able to have a unidirectional current path, which will cause the inconvenience of circuit design. In order to overcome this shortcoming, a novel recessed gate tunnel field-effect transistor with high performance is proposed in this paper and verified by silvaco TCAD software. The effects of process parameters such as doping concentration and geometry dimension on the energy band and properties of the device are analyzed. Simulation results show that the I<sub>on</sub>/I<sub>off</sub> ratio can reach 5×10<sup>6</sup> at a 05V driving voltage and the minimum subthreshold swing of 12mV/dec at the 01V gate to source voltage. In general, this device has a large switching ratio and a very steep subthreshold slope under a low drive voltage. It is expected that this novel device can be one of the promising alternatives for ultra-low power applications.

    Analysis of through silicon via thermal stress induced device mobility variations
    DONG Gang;YAO Yitong;LIU Dang;YANG Yintang
    Journal of Xidian University. 2017, 44(6):  75-78+98.  doi:10.3969/j.issn.1001-2400.2017.06.014
    Abstract ( 376 )   PDF (670KB) ( 195 )   Save
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    This paper studies the mobility variations of the devices placed in different crystal orientations induced by the through silicon via thermal stress. According to the elasticity theory, the mismatch of thermal expansion coefficients between copper and silicon substrate can induce the through silicon via thermal stress, which may cause carrier mobility variations due to the piezoresistive effect. In this paper, a compact analytical model of the through silicon via thermal stress is given based on the planar strain theory. Then the impacts of the through silicon via thermal stress on carrier mobility are presented by using Matlab with the channel direction along[100] and[110], respectively. And the Keep Off Zone is defined for considering the reliability of the device. Finally, we draw a conclusion that the[100] crystal orientation and the[-110] crystal orientation should be preferred as the NMOS device and the PMOS device, respectively.

    Traffic state recognition using static images and FCM
    CUI Hua;YUAN Chao;WEI Zefa;LI Pannong;SONG Xinxin;JI Yu;LIU Yunfei
    Journal of Xidian University. 2017, 44(6):  79-84.  doi:10.3969/j.issn.1001-2400.2017.06.015
    Abstract ( 299 )   PDF (2427KB) ( 182 )   Save
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    Accurate recognition of the traffic condition can proactively alert drivers who will enter the congested road to avoid congestion, so that the degree of congestion will not be increased. And it is also the basis to make scientific decision on active traffic managements, and conducive to alleviate congestion, improve the traffic efficiency, save energy and reduce emission. In this paper, the traffic surveillance videos are sampled every three minutes to build static image database, and the road area is marked as the region of interest (ROI), and then ROI images are normalized in terms of angle and scale. The three image features in ROI, i.e., average gradient, corner and long edge number, are then extracted. Finally, the fuzzy C-means clustering (FCM) method is used to classify the traffic condition into two classifications, i.e., flowing traffic and congestion. Experimental results show that the proposed algorithm can effectively identify the traffic condition involved in the image by the accuracy of 98%. Moreover, compared with the video-based approaches, this method greatly reduces the implementation cost.

    Analysis model of jitter over PTN with time division multiplexing services
    GAO Huisheng;FANG Zixi
    Journal of Xidian University. 2017, 44(6):  85-91+143.  doi:10.3969/j.issn.1001-2400.2017.06.016
    Abstract ( 316 )   PDF (591KB) ( 147 )   Save
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    According to the jitter of the time division multiplexing services of the packet transport network, a random packaging mode and a fixed packaging mode are presented. Two math models for single node and the end-to-end serial path are established. The influence of network parameters, such as background traffic, path node number, node throughput and packaging model is studied. Present results indicates that the delay jitter could be reduced by optimizing these parameters which could provide the basis for configuration of the jitter buffer. The model of fixed packaging has a stronger ability to resist jitter than the model of random packaging.

    New recognition method for binary shortened BCH codes
    LIU Jie;ZHANG Limin;FANG Jun
    Journal of Xidian University. 2017, 44(6):  92-98.  doi:10.3969/j.issn.1001-2400.2017.06.017
    Abstract ( 376 )   PDF (581KB) ( 158 )   Save
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    Current recognition methods are mainly aimed at primitive BCH codes. To solve this problem, a novel recognition method based on soft decision is proposed for binary shortened BCH codes. According to the soft decision information, an analysis matrix is established by the hard decision sequence. The Gauss elimination algorithm is applied to the matrix, and a binary hypothesis test is built to recognize the code length. Then, a primitive BCH code is constructed, and a parity-check matrix is tested under different primitive polynomials by using the soft decision information. Finally, the primitive polynomial and generator polynomial are recognized according to the roots distribution of the generator polynomial. The proposed method is effective for both shortened BCH codes and primitive BCH codes. Simulations verify the applicability of the proposed method. The recognition results of primitive BCH codes show that the proposed method performs better than the conventional recognition methods.

    Low-loss light propagation in the chain of microcavities
    SHI Wenxuan;YUAN Bin
    Journal of Xidian University. 2017, 44(6):  99-102.  doi:10.3969/j.issn.1001-2400.2017.06.018
    Abstract ( 286 )   PDF (877KB) ( 126 )   Save
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    According to the focusing property of the photonic nanojet, the coupling characteristics for the chain of microcavities have been studied. Low-loss light propagation in the chain of microcavities is proposed. The influence of different wavelengths on the intensity of the photonic nanojet and the location of the focal spot are given. Intensity distribution and transmission characteristics for the chain of coupled spherical microcavities are analysed. Simulation results and theoretical analysis show that the chain of spherical microcavities has a highly focused beam and low-loss characteristics because of the focusing effect and backscattering enhancement of the photonic nanojet. A low-loss waveguide can be designed by using these properties of the chain of spherical microcavities. Sub-wavelength focusing of the beam, high optical throughput, and broad spectral transmission properties make the chains of microspheres able to be used in a variety of biomedical applications including minimally invasive and ultraprecise laser surgery.

    Neutrosophic fuzzy clustering segmentation algorithm based on HMRF
    WU Chengmao;SHANGGUAN Ruoyu
    Journal of Xidian University. 2017, 44(6):  103-108+121.  doi:10.3969/j.issn.1001-2400.2017.06.019
    Abstract ( 324 )   PDF (5160KB) ( 216 )   Save
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    Considering neutrosophic C-means clustering algorithm with weak ability of suppressing noise, a neutrosophic C-means clustering segmentation algorithm based on the hidden Markov random field is proposed. First, the hidden Markov random field is used to describe the prior information of the arbitrary pixels classification. Second, information divergence between the prior information and sample classification membership is taken as a regular term and embedded into the existing neutrosophic C-means clustering objective function. Third, the samples in the European Space is mapped into the high-dimensional space through the kernel function, and the iterative expression for the neutrosophic C-means clustering segmentation algorithm based on the hidden Markov random field is obtained by the optimization method. Many standard, actual, and synthetic images corrupted by noise are used to validate the segmentation performance of the improved clustering segmentation algorithm. Experimental results show that the anti-noise performance of the proposed segmentation algorithm is improved significantly than the fuzzy C-means clustering algorithm based on the hidden Markov random field, and other fuzzy clustering segmentation algorithms.

    Low power time-interleaved 12-bit 500MS/s charge-domain ADC
    CHEN Zhenhai;WEI Jinghe;SU Xiaobo;ZOU Jiaxuan;ZHANG Hong;YU Zongguang
    Journal of Xidian University. 2017, 44(6):  109-115+137.  doi:10.3969/j.issn.1001-2400.2017.06.020
    Abstract ( 309 )   PDF (2042KB) ( 239 )   Save
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    A feed-forward common-mode(CM) charge compensation circuit and a foreground calibration technique for the high speed charge-domain (CD) pipelined analog-to-digital converter (ADC) is presented to solve the problem that the precision of CD pipelined ADCs is restricted by the variation of the input CM charge and the offset error. The proposed compensation circuit and the calibration technique can compensate the CM charge and errors caused by the variation of the input CM charge and offset respectively. Based on the feed-forward CM charge compensation circuit and the offset error foreground calibration technique, a 12bit 500MS/s time-interleaved CD pipelined ADC is designed and realized in a 1P6M 018μm CMOS process. The ADC achieves the spurious free dynamic range (SFDR) of 775dB and the signal-to-noise-and-distortion ratio (SNDR) of 627dBFS for a 199MHz input at a full sampling rate. The variation of signal-to-noise ratio is less than 3dB for the input CM voltage in the 0 to 12V range. The power consumption of the prototype ADC is only 220mW at 18V supply and occupies the active die area of 624mm<sup>2</sup>.

    Research on adaptive notch filter cascading neural network anti-jamming algorithm
    YANG Qiong;ZHANG Yi;TANG Chengkai
    Journal of Xidian University. 2017, 44(6):  116-121.  doi:10.3969/j.issn.1001-2400.2017.06.021
    Abstract ( 405 )   PDF (601KB) ( 144 )   Save
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    Satellite navigation suffers from performance degradation in the presence of narrowband interference. We present a Global Positioning System(GPS) receiver anti-jamming algorithm based on the neural network. The method combines the adaptive notch filter with the Back Propagation(BP) neural network. We first use the two order lattice infinite impulse response adaptive notch filter to eliminate-out-of-band jamming, then use the BP neural network predictor to estimate and cancel jamming. We analyze three aspects of algorithm performance which include acquired satellite numbers,signal-to-noise improvements and iteration numbers. Simulation results show that the method can effectively suppress narrowband interference and has a better anti-jamming capacity and a faster convergence speed.

    Iterative beamforming method for the millimeter wave phased array
    TANG Junlin;ZENG Yuan;YUE Guangrong;LI Shaoqian
    Journal of Xidian University. 2017, 44(6):  122-128.  doi:10.3969/j.issn.1001-2400.2017.06.022
    Abstract ( 258 )   PDF (652KB) ( 221 )   Save
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    This paper presents an iterative beamforming method for the millimeter wave phased array. This method uses the approximate orthogonal property for the different paths in the millimeter-wave channel in the case of a large array, and obtains the path with the largest gain in the millimeter-wave channel by iteratively sending the received signal to the other side. The array responses correspond to the path with the maximum gain are used as a beamforming vector for both the transmitter and receiver. Simulation results show that the spectral efficiency obtained by this method is close to the spectral efficiency obtained by the singular value decomposition(SVD) method and has a performance promotion compared with the existing IEEE802.15.3c method. The proposed method has a fast convergence rate and convergence is generally obtained in 3 iterations.

    Research on the non-cooperative game strategy of suppressing IADS for multiple fighters cooperation
    LI Qiuni;YANG Rennong;LI Haoliang;ZHANG Huan;FENG Chao
    Journal of Xidian University. 2017, 44(6):  129-137.  doi:10.3969/j.issn.1001-2400.2017.06.023
    Abstract ( 444 )   PDF (1042KB) ( 178 )   Save
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    A distributed virtual learning game strategy is proposed for the problem on the offense and defensive game of the Suppression of Integrated Air Defense System (IADS) by multiple fighters  cooperation. By modeling the combat resources as multi-agents networks nodes, a complicated operational process integrating kind of different combat resources and accompanying detecting, jamming and attacking is researched. Considering the evaluations of threats, the evaluations of the economic strategy value and the influence of the task payment on the whole system, a profit model is developed for both offense and defensive sides under the confrontation game, and the Mixed Strategy Nash Equilibrium (MSNE) with n-person and n-strategy in the system countermeasures is solved by using this model. In our designed approach, the problem of dynamic changing of the numbers and positions for the nodes in the operational process is overcome, and the appropriate strategy can be chosen from the large profit space. Simulation results demonstrate the advantages of the designed approach in the respects of self-optimizing and self-organizing on tactical re-planning in the real time, and it is also shown that the designed approach can achieve the maximum of expected payoffs and effectively solve the problem of suppressing IADS for multiple fighters cooperation.

    Dynamic reliability analysis of spacial flexible beam
    JIN Hongling;GUO Chengyang;CHEN Jun;CHEN Jianjun
    Journal of Xidian University. 2017, 44(6):  138-143.  doi:10.3969/j.issn.1001-2400.2017.06.024
    Abstract ( 255 )   PDF (709KB) ( 168 )   Save
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    In order to investigate the dynamic response reliability of the spacial flexible beam, the Monomial Cubature Rules (MCR) based Stochastic Response Surface Method (SRSM) is applied to derive the surrogate model of the nonlinear implicit limit state function. A small set of sample pairs for flexible beam dynamic response is generated by taking the integral points of MCR as sample points. Based on these sample pairs and SRSM, the surrogate model of the implicit limit state function is established. The results show that the proposed method has an excellent performance in terms of accuracy and efficiency compared with the Probabilistic Collection Method (PCM) based SRSM and Monte Carlo method, and that the dispersion of system parameters has a significant effect on the dynamic response reliability of the spacial flexible beam.

    Passive browser identification based on the packet length
    LIU Changjiang;WAN Jian;HAN Jiesi;WEI Qiang
    Journal of Xidian University. 2017, 44(6):  144-149.  doi:10.3969/j.issn.1001-2400.2017.06.025
    Abstract ( 267 )   PDF (544KB) ( 181 )   Save
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    The browser, as the most frequently used network application software, is an important target of hackers. For network administrators, mastering the browsers used by network users can help them to discover the possible vulnerabilities in the host computers and take defensive measures expediently. In this paper, we propose a passive browser identification method by requesting the packet length. We make use of the difference in requesting the packet length when using different browsers to request the web content, and then achieve the browser identification by the clustering algorithm. The experiment shows that the recognition rate of the five most common browsers can reach more than 90% in this way, and the time stability of the fingerprinting is also confirmed. This method does not increase the network traffic or interfere with the normal operation of the network, and it can identify web browsers under the condition of both non-encryption and encryption.

    Global sparse gradient coupled tensor diffusion model for image denoising
    ZHANG Rui;FENG Xiangchu;YANG Lixia;CHANG Lihong
    Journal of Xidian University. 2017, 44(6):  150-155.  doi:10.3969/j.issn.1001-2400.2017.06.026
    Abstract ( 326 )   PDF (4195KB) ( 202 )   Save
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    A global sparse gradient coupled tensor diffusion model for image denoising is proposed to improve the problem of edges blurring induced by the DTTR model. First, a tensor matrix is constructed by the global sparse gradient which is more accurate and robust than classic gradient operators. Then the diffusion equation is guided by the tensor matrix for image denoising. The diffusion resulting from this model is isotropic inside a homogeneous region and anisotropic along its edge so that an accurate tracking of the edges is possible. Numerical experiments show that the proposed method achieves a competitive denoising performance in comparison with the comparative algorithms in terms of both subjective and objective qualities. Experimental results indicate that the performances of denoising methods can be improved by introducing a guide map, which is obtained by the global sparse gradient model.

    Provable multi-copy dynamic data possession in cloud storage
    REN Jingsi;WANG Jinlin;CHEN Xiao;YE Xiaozhou
    Journal of Xidian University. 2017, 44(6):  156-161+174.  doi:10.3969/j.issn.1001-2400.2017.06.027
    Abstract ( 380 )   PDF (579KB) ( 155 )   Save
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    In the cloud storage paradigm, verifying the integrity of multiple remote copies is inefficient, and dynamic data updates are not supported. To solve this problem, we first propose a multi-copy integrity checking model for the distributed cloud storage system, and then design a multi-copy provable data possession scheme based on the bilinear map and pseudo-random mask technique. Aiming at updating multiple copies, each data block is mapped to an entry in the seed mapping table. Security analysis and performance evaluation show that our scheme is correct and complete, and can significantly improve efficiency.

    Emotional speech feature extraction and optimization of phase space reconstruction
    SUN Ying;SONG Chunxiao
    Journal of Xidian University. 2017, 44(6):  162-168.  doi:10.3969/j.issn.1001-2400.2017.06.028
    Abstract ( 358 )   PDF (1645KB) ( 193 )   Save
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    In view of the imperfection of the existing speech emotional characteristics in the representation of emotional information, this paper introduces phase space reconstruction theory into the feature extraction of emotional speech. By analyzing the geometrical characteristics of phase space reconstruction under different speech emotion states, five nonlinear geometric features of trajectory-based descriptive contours under the reconstructed phase space are extracted as the new emotional speech characteristic parameters, and a novel feature parameter optimization method based on the relationship of emotional speech feature mapping is proposed. First, experience uses four basic emotions of happy, sad, neutral and angry in the German Berlin voice library as a sample. Second, the nonlinear geometric features and nonlinear attribute features (Minimum delay time, dimension correlation, Kolmogorov entropy, and Maximum Lyapunov exponent and Hurst exponent) are extracted from the emotional speech signal. Finally, a linear support vector machine (SVM) is employed to classify emotional speech signals according to the design scheme. The results show that the nonlinear geometric features have a strong dominance in the emotional speech recognition compared with the nonlinear attribute, and that the method of feature parameter optimization can obtain the optimal nonlinear feature set when nonlinear geometric features are combined with nonlinear attribute features,which verifies the practicability of the method.

    Low-profile circularly polarized antenna using the half-mode circular substrate integrated waveguide technique
    ZHANG Yefeng;ZHU Yongzhong;LIU Mingfei;LU Hongyan
    Journal of Xidian University. 2017, 44(6):  169-174.  doi:10.3969/j.issn.1001-2400.2017.06.029
    Abstract ( 323 )   PDF (1463KB) ( 232 )   Save
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    A technique to design a compact half mode substrate integrated circular cavity (HMSICC) cavity backed antenna is presented. The proposed antenna achieves left-handed circularly polarized(LHCP) using a crossed slot. The feeding strip-line loaded stub in the middle metallization layer and the S-shaped slot in the bottom metallization layer can achieve a better impedance match. Measured results show that the prototype achieves a bandwidth of 73% for 10dB return loss and that the axial ratio(AR) bandwidth is at least 16% with the maximum gain of 62dBi.